1. Field of the Invention
The present invention relates generally to a method of transmitting data among a plurality of LSIs (Large Scale Integrated Circuits) which are connected to one another through an external bus, and more particularly, to a method of transmitting, in a DVD (Digital Versatile Disk) audio reproducing apparatus comprising a digital signal processing LSI and a D/A (Digital-to-Analog) converting LSI which are connected to each other through an external bus, a digital signal from the digital signal processing LSI to the D/A converting LSI through the external bus, and the DVD-Audio reproducing apparatus using the method.
2. Description of the Background Art
In recent years, A DVD-Audio standard for realizing multi-channel reproduction of a high-quality sound by recording mainly an audio signal on a DVD having a capacity of 4.7 GB in a single-sided one layer system has been determined, and a DVD-Audio reproducing apparatus for reproducing a DVD-Audio disk has been developed.
In the DVD-Audio standard, audio signals having various sampling frequencies, various numbers of quantization bits, and various numbers of channels can be recorded and reproduced. For example, an audio signal having a sampling frequency of 192 kHz, 24 quantization bits, and two channels can be recorded to reproduce a stereo sound having a maximum frequency of 96 kHz. Alternatively, an audio signal having a sampling frequency of 96 kHz, 24 quantization bits, and six channels can be recorded to reproduce a multi-channel sound having a maximum frequency of 48 kHz. Further, a variety of recording and reproduction can be performed. For example, a video signal is recorded on the DVD to reproduce an image together with a sound.
Examples of the sampling frequency of the audio signal include 192/96/48 kHz and 176.4/88.2/44.1 kHz. An example of the quantization bits are 24/20/16 bits.
FIG. 11 is a diagram showing the configuration of a portion related to the transmission of a digital signal from a digital signal processing LSI 6 to a D/A converting LSI 7 in a conventional DVD-Audio reproducing apparatus.
In FIG. 11, the digital signal processing LSI 6 and the D/A converting LSI 7 are connected to each other through external buses 13 to 15. The digital signal processing LSI 6 processes an incoming digital signal (a packet stream) , to generate a digital signal. The D/A converting LSI 7 converts the digital signal outputted from the digital signal processing LSI 6 into an analog signal.
FIG. 12 is a timing chart showing the digital signal outputted from the digital signal processing LSI 6 shown in FIG. 11 (in a case where the number of channels is 2). In FIG. 12, a word clock is a clock signal representing the timing at which channels in serial data are switched, and is transmitted through the external bus 13 shown in FIG. 11. The serial data includes data representing two channels (ch1 and ch2), and is transmitted through the external bus 14 (when the number of channels is four, for example, another serial data including two channels (ch3 and ch4) is outputted in parallel with the serial data). A bit clock is a clock signal which is synchronized with the serial data, and is transmitted through the external bus 15. A bit array {MSB, 23,22, , . . . , LSB} on each of the channels ch1 and ch2 is obtained from the word clock, the serial data, and the bit clock.
As described above, in the conventional DVD-Audio reproducing apparatus, the digital signal processing LSI 6 and the D/A converting LSI 7 are provided on separate chips, and are connected to each other through the external buses 13 to 15. Therefore, the digital signal can be taken out of the external buses 13 to 15 between the digital signal processing LSI 16 and the D/A converting LSI 7 and unfairly copied. An ultrahigh-quality stereo sound and a high-quality multi-channel sound, as described above, can be easily reproduced from the digital signal immediately before being inputted to the D/A converting LSI 7 (see FIG. 12).
If the digital signal processing LSI 6 and the D/A converting LSI 7 are provided on a single chip, it is possible to prevent the digital signal from being taken out of the external buses 13 to 15 and unfairly copied. In this case, however, noises and the like due to digital signal processing performed on the digital signal processing LSI 6 are included into an analog circuit portion included in the D/A converting LSI 7. As a result, another problem occurs. For example, the quality of an analog signal outputted from the D/A converting LSI 7 is degraded. When a DVD-Audio is reproduced, higher-speed digital signal processing (as compared with that in CD reproduction, for example) is performed, so that the quality is significantly degraded.
Therefore, an object of the present invention is to provide a DVD-Audio reproducing apparatus capable of preventing a digital signal immediately before being inputted to a D/A converting LSI from being taken out and unfairly copied.
The present invention has the following features to solve the problem above.
A first aspect of the present invention is directed to a method of transmitting data between a first LSI and a second LSI which are connected to each other through an external bus, characterized by comprising the steps of:
scrambling the data inside the first LSI;
transmitting the scrambled data from the first LSI to the second LSI through the external bus; and
descrambling the scrambled data inside the second LSI.
In the first aspect, the signal transmitted through the external bus between the first LSI and the second LSI is scrambled. Accordingly, even if the data is taken out of the external bus and unfairly copied, the data cannot be reproduced.
A second aspect is directed to a method of transmitting, in a DVD-Audio reproducing apparatus comprising a digital signal processing LSI and a D/A converting LSI which are connected to each other through an external bus for reproducing a DVD-Audio disk, a digital signal from the digital signal processing LSI to the D/A converting LSI through the external bus, comprising the steps of:
inside the digital signal processing LSI,
processing the digital signal which has been read out of the DVD-Audio disk; and
scrambling the digital signal which has been processed;
transmitting the scrambled digital signal from the digital signal processing LSI to the D/A converting LSI through the external bus;
inside the D/A converting LSI,
descrambling the scrambled digital signal transmitted through the external bus; and
converting the digital signal which has been descrambled into an analog signal.
In the second aspect (and in the following third aspect), the digital signal transmitted through the external bus between the digital signal processing LSI and the D/A converting LSI is scrambled. Accordingly even if the digital signal is taken out of the external bus and unfairly copied, the digital signal cannot be reproduced.
A third aspect is directed to a DVD-Audio reproducing apparatus for reproducing a DVD-Audio disk, comprising
a digital signal processing LSI and a D/A converting LSI which are connected to each other through an external bus,
the digital signal processing LSI comprising
digital signal processing means for processing a digital signal which has been read out of the DVD-Audio disk, and
scrambling processing means for scrambling the digital signal outputted from the digital signal processing means,
the D/A converting LSI comprising
descrambling processing means for descrambling the scrambled digital signal transmitted through the external bus, and
D/A conversion means for converting the digital signal outputted from the descrambling processing means into an analog signal.
According to first embodiment, the apparatus further comprising:
header reading means for reading attribute information relating to a digital signal, which has been read out of the DVD-Audio disk, described in a header attached to each of packets composing the digital signal;
a header analysis portion for analyzing the attribute information which has been read by the header reading means; and
scrambling/descrambling control means for controlling the scrambling processing means and the descrambling processing means on the basis of the result of the analysis by the header analysis portion.
In the first embodiment, scrambling/descrambling corresponding to the attribute of the digital signal is performed.
According to a first exemplary embodiment,
the attribute information includes information relating to the quality of a sound obtained by reproducing the digital signal (hereinafter referred to as the quality of the digital signal), and
the scrambling/descrambling control means controls the scrambling processing means and the descrambling processing means on the basis of the quality of the digital signal which is represented by the result of the analysis by the header analysis portion such that secrecy conforming to the quality of the digital signal is realized.
In the first exemplary embodiment, scrambling/descrambling is performed such that secrecy conforming to the quality of the digital signal is realized (for example, the higher the quality of a signal is, the higher the secrecy to be realized by the signal is). As a result, the efficiency of scrambling/descrambling processing also improves.
According to first specific exemplary embodiment, the quality of the digital signal is the sampling frequency and/or the number of quantization bits of the digital signal.
According to a second specific exemplary embodiment,
the scrambling/descrambling control means
has a table in which qualities at a plurality of levels which are previously determined with respect to the digital signal and identifiers assigned to a plurality of scrambling/descrambling information for realizing secrecy conforming to each of the qualities are described with a one-to-one correspondence established therebetween, and the plurality of scrambling/descrambling information,
refers to the table, to select the scrambling/descrambling information corresponding to the quality of the digital signal which is represented by the result of the analysis by the header analysis portion, and
feeds the selected scrambling/descrambling information to the scrambling processing means and the descrambling processing means, to control the scrambling processing means and the descrambling processing means.
According to a more specific exemplary embodiment, the scrambling/descrambling control means comprises:
a scrambling/descrambling information selection portion having the table, and referring to the table to select the scrambling/descrambling information corresponding to the quality of the digital signal which is represented by the result of the analysis by the header analysis portion and outputting the identifier assigned to the selected scrambling/descrambling information;
a scrambling control portion having the plurality of scrambling information, and feeding to the scrambling processing means the scrambling information corresponding to the identifier which has been outputted by the scrambling/descrambling information selection portion out of the plurality of scrambling information; and
a descrambling control portion having the plurality of descrambling information, and feeding to the descrambling processing means the descrambling information corresponding to the identifier which has been outputted by the scrambling/descrambling information selection portion out of the plurality of descrambling information,
the scrambling control portion being included inside the digital signal processing LSI, and the descrambling control portion being included inside the D/A converting LSI.
In the more specific exemplary embodiment, the scrambling control portion having the plurality of scrambling information is included inside the digital signal processing LSI, and the descrambling control portion having the plurality of descrambling information is included inside the D/A converting LSI. Accordingly, the scrambling/descrambling information does not leak. As a result, the digital signal which has been unfairly copied cannot be reproduced.
According to a third specific exemplary embodiment, the attribute information includes information indicating which position is the boundary of tracks in the digital signal, and
the scrambling/descrambling control means has a plurality of scrambling/descrambling information, and selects any one of the plurality of scrambling/descrambling information in units of tracks in response to an instruction by a user and feeds the selected scrambling/descrambling information to the scrambling processing means and the descrambling processing means.
In the third specific exemplary embodiment, the boundary between a track (corresponding to a piece of music) and another track is detected, to select the scrambling/descrambling information in units of tracks upon receipt of the instruction by the user.
According to a fourth specific exemplary embodiment,
the attribute information includes information indicating which position is the boundary of groups in the digital signal, and
the scrambling/descrambling control means has a plurality of scrambling/descrambling information, and selects any one of the plurality of scrambling/descrambling information in units of groups in response to an instruction by a user and feeds the selected scrambling/descrambling information to the scrambling processing means and the descrambling processing means.
In the fourth specific exemplary embodiment, the boundary between a group (corresponding to one album comprising a plurality of pieces of music) and another group is detected, to select the scrambling/descrambling information in units of groups upon receipt of the instruction by the user.
According to a second embodiment, the scrambling processing means scrambles the digital signal outputted from the digital signal processing means in units of sample points for each channel.
According to a third embodiment, the scrambling processing means scrambles the digital signal outputted from the digital signal processing means in units of bytes for each channel.
According to a fourth embodiment, the scrambling processing means scrambles the digital signal outputted from the digital signal processing means in units of sample points between channels.
According to a fifth aspect, the scrambling processing means scrambles the digital signal outputted from the digital signal processing means in units of bytes between channels.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.